This paper deals with the experimental implementation of one of the methods for the determination of cardiac output – the dye dilution. Measurement is performed on a mechanical model of the cardiovascular system. It is a specific and experimental measurement intended mainly for educational purposes. It was created a real model of bloodstream at author’s workplace. The model enables to set a pulsatile flow of the fluid with defined pressure and flow rate. This experiment is to demonstrate the principle of determination of cardiac output using the dilution methods. This paper is focused only on measuring by dye dilution method. The measurement results are verified by using a Doppler sonography and volumetric containers.
The cardiac output is a very important parameter that
helps to diagnose cardiac insufficiency. The
determination of cardiac output can be performed using
low precision and limited non-invasive methods or
high precision but costly and painful invasive methods.
Basic non-invasive methods are Doppler sonography,
bio-impedance cardiography and mathematical
analysis. Educational demonstration of non-invasive
measurement methods is very easy.
Invasive methods of measurement cannot be
demonstrated on human being for educational
purposes. Based on this fact a mechanical model of the
cardiovascular system was developed. The model
allows demonstrating the invasive measuring of
bloodstream heamodynamic parameters.
This paper focuses primary on the determination of
the cardiac output, detailed description of the
mechanical model has been published. [1,2]
Principle of dilution methods
The fundament of dilution methods for determination
of cardiac output is dilution of the injected substance in
the blood. A substance can be special dye or saline
with a defined concentration and temperature. There
are two types of dilution measurements: the dye
dilution method and the thermodilution method. [4,7]
This method involves the continuous measurement of
the temperature of the pre-cooled blood. The clinical
measurement is performed by the Swanz-Ganz
catheter. This instrument provides cold saline (4 °C)
injected into the blood and then distanced blood
The result of this process is the thermodilution curve
whose mathematic analysis gives value of the Cardiac
Dye dilution method
The Dye dilution method is based on the measuring
of the light absorbance of the dye injected into the
blood. The dye (Indo-Cyanine Green) is injected by
special pulmonary catheter. Dyed blood is continuously
sucked into the absorption photometer.
The result is the dilution curve of the relative
concentration of the dye diluted with the blood.
Analysis according to equation (1) gives value of the
Cardiac Output. [4,7]
Mechanical model of the
The mechanical model of the cardiovascular system
was developed for educational purposes at author’s
workplace. It consists of tubes, valves and
a mechanical pump (see Fig. 1). [1,2,5,6]
Various types of the tubes are used for the
construction of the arterial, venous and capillary
bloodstream. The parameter compliance of the tubes is
very important for correct function of the model.
Venous vessels are rigid and arterial vessels are elastic.
Hydraulic resistance of the bloodstream is controlled
by regulated valve. Aortic valve and minor venous
valves are demonstrated by the check valves.
The heart is constructed using a mechanical gear
pump. The pump is driven by the pulse mode using
special control unit consists of the microprocessor and
switching devices. It is possible to choose optional
heart rate and heart ratio (power of the pump). [1-3,5]
Experimental measurement of the
Selection of the type of the dye and its spectral band
First of all, it was necessary to choose the right type
of the dye and to tune a suitable spectral wavelength of
the photometer. The photometer was constructed of
a pair of the IR diode and IR photodiode (λ = 900 nm). It is given by wide availability of these components.
Spectral analysis of different types of the dye proved
a suitability of the use the Copper sulfate (see Fig. 2).
Design of the measuring apparatus
The light source is an infrared light emitting diode
with maximum intensity at 900 nm wavelength. For the
first experiment it was fully sufficient to supply the
light source by constant current. The light passes
through arterial vessel and excites the light detector.
The detector is light-sensitive diode with maximum
sensitivity at 900 nm wavelength. The photodiode
operates at the photovoltaic mode. The output voltage
is dependent on light intensity on the detector. The
output voltage is amplified by an op-amp and then is
sampled into the digital form.
Clean fluid flow does not affect to passage of the
infrared beam. The fluid flow with injected dye causes
attenuation of the IR beam. It is dependent on
concentration of the dye with the fluid.
Signal processing and data analysis
The data processing is performed by the Matlab
script. Firstly, the data was loaded and the useful
components were separated. For very credible
demonstration it is measured also blood pressure curve.
The data must be converted to the pressure scale.
The calculation of the cardiac output according to the
equation (1) is valid only with relative values of the
concentration. Reference values are used to relative
scale conversion. The reference minimum is the
attenuation of the clean fluid flow. The reference
maximum is the attenuation of the dye liquid only.
The relative concentration curve is integrated using
the cumulative sum. The proportion of the injected dye
volume and cumulative sum of the relative
concentration values is equal to the cardiac output.
Results of the measuring
Measuring is usually carried out with various settings
of the Heart rate and the Heart Ratio parameters. The
validation of the results is ensured by the measuring
using the Doppler sonography and the volumetric
containers. [1,2] The verification is carried out at the
same Heart Rate and Heart Ration parameters. Test
measurement was performed tree times for each
parameter of the model. The results are shown in
The Matlab script plots dye dilution curve and
pulsatile blood pressure curve to the educational
compared (see Fig. 4). On the figure is clearly
noticeable time point of the dye injection.Verification methods
This paper is not targeted at the detailed description
of the model CVS or Doppler sonography
measurement. The next section deals only brief
description of the verification methods using Doppler
sonography and volumetric containers.
Validation using volumetric containers is very simple
and indisputable. It is monitored the quantity of the
liquid, which passed through the pump per minute. The
accuracy of the validation depends on the correct
calibration of the measuring scale of the container.
Validation using Doppler sonography is very similar
to clinical determination of the cardiac output. The
probe is attached on the tube within fluid flow. This
leads to record a velocity profile of the fluid flow (see
Fig. 5). The integration of this profile and cross section
area multiply give a value of the cardiac output. The
data processing performs Doppler sonography device
The simple model of the cardiovascular system was
developed for educational purposes. The model is able
to simulate pulsatile fluid flow. Students can measure
invasive pulse pressure curve, cardiac output by
invasive and non-invasive methods (the doppler
sonography and the dye dilution).
The presented method helps the better and the
practical understanding of the invasive measurement of
the cardiac output, because it is very similar to the
clinical determination of the cardiac output. This
exercise learns to apply the theoretical equations into
the practical measurement.
Relative accuracy of the measurement of the cardiac
output is about 15 %. Moreover, it is possible to watch
the difference of laminar and turbulent flow by the
sonography method on the model.
This work has been supported by the grant No.
F3a 2177/2012 presented by University Development
Foundation and also by the research program No.
MSM 6840770012 of the Czech Technical University
in Prague (sponsored by the Ministry of Education,
Youth and Sports of the Czech Republic).
Department of Circuit
Faculty of Electrical Engineering
Czech Technical University in Prague
Technická 2, CZ-166 27 Prague
Phone: +420 224 355 869
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